In recent years, the number of installations involving doors secured by electric locking devices has been increasing rapidly as part of the growth of the security market. Most installations of electric locks on doors consider that one side of the door constitutes a "protected area". Persons within this area can freely use the door for egress at any time. Indeed, building codes often require that free egress from the protected area be allowed by the equipment on the door. Entry from outside the protected area is generally restricted and various arrangements are used to insure that the person entering is authorized to do so. These arrangements include card reader systems, digital keypads, keyswitches and remote release after audio communication via an intercom or surveillance with a television camera.
If the electric locking device on the door is an electric strike, free egress is accomplished simply by turning a doorknob which retracts the latch from the electric strike. In other instances, a mechanical panic bar can be depressed to retract the latch. Increasingly, however, users demand higher security electric locking devices which are more capable of resisting a physical assault on the door. These devices include electric solenoid deadbolts and electromagnetic locks including a large electromagnet and a strike plate or armature.
Free egress from a door secured by an electric solenoid deadbolt or electromagnetic lock must include a switch changing state. Purely mechanical means will not release an electric lock. In some instances, a simple push button may be mounted alongside the door, but this is a poor solution, as a person wishing to exit may not know the function of the push button and the person will certainly not find it in a panic situation or in a situation where the lights have gone out. The product of choice, therefore, to allow free egress on a door equipped with an electric lock is a panic bar to which an electromechanical snap switch has been added such that depressing the bar activates the switch which, in turn, releases the electric lock.
Panic bars with switches however, suffer from a number of disadvantages. There are numerous moving parts which render the product costly to manufacture and highly subject to wear-related failure. Also, in a real panic situation, persons may become wedged against the door in such a way that the bar is jammed so that it cannot move. If the bar cannot move, it will not function to depress the switch.
The present invention seeks to replace switch equipped mechanical panic bars with an all electronic device. The present invention has no moving parts and does not suffer mechanical wear so that it has a much longer operating life and in general can be cheaper to manufacture. It will also function more reliably in a true panic situation as the risk of people getting wedged against the bar and therefore immobilizing it will not stop a touch sensitive bar from releasing the lock. Another benefit of the present invention is the redundant push switch which constitutes a secondary means of operation in the remote event that the sensor will fail.
Prior patents which have some relevance to the present invention include U.S. Pat. No. 4,682,801, issued July 28, 1987, and assigned to the assignee of this patent application. This patent is an electromagnet access control circuit and shows a circuit and a physical arrangement for an electromagnet and striker plate or armature locking arrangement. R. W. Forsberg, U.S. Pat. No. 3,495,353, granted Feb. 7, 1970, discloses the use of a touch plate beside a door, to energize a motor to open the door when the touch plate is touched. J. A. Wisnia, U.S. Pat. No. 3,496,381, granted Feb. 17, 1970, discloses a capacitive plate located in a position similar to a floor mat, and, like the Forsberg system causes the door to open when the capacitance increases by the presence of a person. Two patents relating to alarm systems which are energized by increased capacitance on a doorknob, are Sweeney, U.S. Pat. No. 4,168,495, granted Sept. 18, 1979, and H. C. Lam, et al., U.S. Pat. No. 4,287,513, granted Sept. 1, 1981. The foregoing patents have a certain subject matter which is vaguely related to the present invention, but none of them discloses a system which solves the problems as outlined hereinabove in the preceding paragraphs.